The present invention provides a robot arm. The robot arm is for forking a substrate, and includes: a substrate fork and vacuum cups. The substrate fork includes parallel spaced prongs, and an upper surface of each prong is provided with vacuum cups spaced along an extending direction of the prong; and vacuum cups on two prongs at outermost sides of the substrate fork are scratch-resistant vacuum cups, and a top face and a side face of each scratch-resistant vacuum cup are connected through an arc-shaped surface. By setting the top face of the scratch-resistant vacuum cup connected to the side face through the arc-shaped surface, when the substrate is bent with the gravity, the contact area between the substrate and the scratch-resistant vacuum cup can be increased, to improve the friction therebetween, prevent the substrate from being scratched in a transportation process, and ensure the security of substrate transportation.